Simulation of the nanoindentation test of a (001) single crystal of Cu is performed using 3D4 modelling. A nucleation criterion for the indent induced dislocations has been established from experiments. The dislocation microstructure at a depth of 50nm is shown in the animated sequence. Hardness is estimated from the dislocation density. Both the indent-induced plastic size and the Hardness estimation fit well the experiments performed under the same conditions.